Just as proteins and carbohydrates are made of smaller components, so are fats. Most of the stored fat in our bodies (body fat) and fat found in food (dietary fat) exist in a form called triglycerides. These are made up of three individual fatty acids that are connected together by another molecule, glycerol.
Also, you may often hear the terms saturated, monounsaturated, and polyunsaturated in relation to fat and wonder what they really mean. The saturation refers to the chemical bonds of the fatty acid molecules. Saturated fats tend to be a bit more solid at room temperature and are found in many animal foods, such as higher-fat cuts of beef, lamb, veal, pork, and poultry; butter; cream; full-fat and 2 percent milk; cheese; and full-fat yogurt. Saturated fat, in a more liquid form, also occurs in coconut and palm oils. Our bodies can handle saturated fat; however, eating too much may increase inflammation throughout the body and blood cholesterol levels. High saturated fat intake is associated with other health problems, such as diabetes and some forms of cancer. The American Heart Association allows for 7 percent of total calories to come from saturated fat (16 grams in a 2,000-calorie diet).
Monounsaturated fats are found in foods such as olive oil, canola oil, peanuts and peanut oil, most nuts (except walnuts), and avocados. Sometimes they are also referred to as omega-9 fatty acids. People refer to monounsaturated fat as a “good” fat because it plays a role in keeping our hearts healthy.
Polyunsaturated fats are further designated by their structures: omega-3 and omega-6 fatty acids. The omega-3 fats are found in many varieties of fish and also in some plant foods: flaxseed, walnuts, and canola oil. Omega-6 fatty acids are found in safflower, sunflower, corn, soybean, cottonseed, and sesame oils. Just as there are essential amino acids that the body needs but cannot make, there are essential fatty acids. The specific omega-6 fatty acid that is essential is named linoleic acid. The omega-3 that is essential is called alpha-linolenic acid. These fats are required to make substances called eicosanoids, which are hormonelike substances that affect blood pressure, immunity, inflammation, contraction of smooth muscle tissue (such as your heart), and more. A small amount of each of the polyunsaturated fats are needed daily.
Trans fat is a type of fat that occurs naturally in small amounts in meats and dairy; there is also a man-made trans fat, which is the type we know to be most harmful to health. The naturally occurring trans fat may actually be handled by the body differently than trans fat found in partially hydrogenated oils, which are artificially created. Partially hydrogenated oils are made when hydrogen is added to oil, which causes it to become solid; examples include margarine and shortening. Originally designed to increase shelf life and add stability to processed foods, we have since learned that trans fats are not healthful and cause good cholesterol (HDL, or high-density lipoprotein) to go down and bad cholesterol (LDL, or low-density lipoprotein) to go up. Artificial trans fat may increase inflammation and has a negative heart health consequence. Unlike saturated fat, there is no need for any artificially created trans fat in the diet. The American Heart Association recommends no more than 1 gram a day of trans fat.
Sterols are substances present in the fatty tissue of plants and animals that have a ring structure instead of a chain. The most well known sterol is cholesterol, which is found only in animal-based foods. Different sterols have different effects in the body. Some sterols in plant foods have actually been isolated and added to salad dressings, made into spreads, and used to fortify drinks to help lower cholesterol. Too much cholesterol in the body may not be healthy, but cholesterol is vital to our well-being. It is necessary to form steroids in the body (the hormones estrogen, androgen, and progesterone as well as the adrenocortical hormones), bile (which is needed to digest fat), and vitamin D. Cholesterol is also in the membranes of all cells in our bodies. Much of the cholesterol we need can be made by our bodies. It is only when we produce too much cholesterol that it becomes problematic to our well-being. Dietary saturated fat consumption has a greater influence on increasing the levels of cholesterol in our blood than does the actual cholesterol content of food. Figure 5.1 shows which foods are sources of the different fats. Many foods contain more than one type of fat; we listed each food under the fat that predominates.
It’s important to make the distinction between dietary fat and body fat. Fat that is eaten serves important functions in the body and is a source of calories. However, dietary fat does not necessarily turn into body fat. Including enough fat in the foods we eat helps food taste good and helps satisfy our appetites. Dietary fat provides nine calories per gram compared with four calories per gram of carbohydrate or protein, so it is a dense source of calories. Exceedingly high-fat diets can crowd out, or not allow us to get enough of, the other macronutrients, protein, and carbohydrate.
Having adequate body fat is also essential for health and performance. Regulating weight is a big concern for many athletes, as is achieving the right ratio of lean mass to fat weight. Although an overfat athlete may feel sluggish, too little body fat can impair hormone production, leading to inadequate muscle building and demineralization of bone.